SKULL BASE REVIEW AND PATHOLOGY

Skull Base Anatomy Review Skull Base Boundaries Upper surface of ethmoid bones and orbital plate of frontal bone to the occiptal bone Three Key Bones Sphenoid Temporal Occipital Complex area Keep it simple

Skull Base Anatomy Review Temporal Bone Temporal bone- petrous portion Sphenoid Bone Occipital Bone Key Fissures Petrosphenoidal fissure Petrooccipital fissure Key Sutures Sphenosquamous Suture Occipitomastoid Suture Guidance for geography Don’t mistake for fx

Skull Base Anatomy Review Key Openings Foramen spinosum Foramen ovale Foramen lacerum Foramen rotundum Foramen magnum Foramen of vesalius Jugular foramen Superior orbital fissure Inferior orbital fissure Optic canal Vidian canal Hypoglossal canal Pterygopalatine fossa 7 foramina 2 fissures 3 canals All with fun stuff inside.

Skull Base Anatomy Review

Skull Base Anatomy Review Sphenoid spine- lower level Foramen rotundum- higher level Pterygopalatine fossa Foramen ovale Petro-occipital fissure Pterygoid canal f. lacerum Foramen spinosum

Skull Base Anatomy Review Foramen magnum Medulla oblongata Vertebral arteries Anterior/Posterior spinal arteries Hypoglossal canal CN XII Hypoglossal artery Hypoglossal artery = not always present. Sometimes, can have a small emissary vein that runs through here that can protrude into the cerebellomedullary cistern and mimic a nerve sheath tumor. * *

Skull Base Anatomy Review Jugular Foramen Pars nervosa: CN IX, inferior petrosal sinus Pars vascularis: CN X, XI, jugular bulb * 2 parts: Pars nervosa = anteromedial Pars vascularis aka pars venosa = posterolateral Separated by the jugular spur. Pars nervosa: glossopharyngeal nerve, inferior petrosal sinus- runs along petrooccipital fissure Pars vascularis: vagus and spinal accessory nerve Jugular bulb: confluence b/w sigmoid sinus and internal jugular vein. Anterolateral to pars nervosa = petrous portion of the carotid artery. * Carotid canal

Skull Base Anatomy Review Foramen Spinosum Middle meningeal artery/vein CV V3, recurrent branch Lesser superficial petrosal nerve Foramen Ovale CN V3 Lesser petrosal nerve Accessory meningeal artery Emissary veins Foramen of Vesalius Emissary vein Accessory meningeal artery- asc intracranial branch F.S.: V3 recurrent = mandibular branch. Emissary veins in FS and FO connect cavernous sinus with pterygoid plexus of veins = path for nasaopharyngeal tumors. Foramen of vesalius- inconstant. Anterior and medial to f. ovale. When it does occur, it contains (read slide)

Skull Base Anatomy Review Foramen Lacerum Ascending pharyngeal artery- meningeal branch Nerve of pterygoid canal Vidian Canal aka pterygoid canal Pterygopalatine fossa - foramen lacerum Vidian nerve Vidian artery F.L.:read slide Vidian canal = aka pterygoid canal. Connects pterygopalatine fossa to foramen lacerum. Contains vidian artery (branch of maxillary artery) and nerve. Vidian nerve = formed by merger of greater superficial petrosal nerve (branch of facial nerve) and deep petrosal nerve.

Skull Base Anatomy Review Foramen rotundum CN V2 Artery of foramen rotundum Emissary veins

Skull Base Anatomy Review Pterygopalatine Fossa Pterygopalatine ganglia V2 Pterygopalatine plexus Communicates with: Inferior orbital fissure Orbital apex Sphenopalatine foramen Pterygomaxilary fissure Foramen rotundum Vidian canal Greater/lesser palatine canals and foramina PPF = conduit for spread of tumor and infection Communicates with inf orbital fissure, orbital apex,… PPF - Sphenoplatine foramen = to nasal fossa PPF – pterygomaxillary fissure = to masticator space PPF- foramen rotundum = connection with Meckel’s cave, cavernous sinus PPF- Vidian canal = to foramen lacerum PPF- to greater/lesser palatine canals = to palate

Skull Base Anatomy Review Cavernous Sinus Receives: Superior opthalmic vein Inferior opthalmic vein Sphenoparietal sinus Drains via: Petrosal sinuses Basilar plexus Pterygoid plexus Connection: Circular sinus Contains: CN III, IV, V1, V2, VI PPF – foramen rotundum = connection with meckel’s cave, cav sinus, since we’ve mentioned it a few times now and b/c contains a lot of key elements: Cav sinus- read slide. V2- lateral wall of CS- then to foramen rotundum V1- lateral wall of cav sinus- then to superior orbital fissure, along with CN III, IV, VI Meckel’s Cave Posterior aspect of cavernous sinus Gasserian ganglion (sensory root ganglion of CN V)

Skull Base Anatomy Review Superior Orbital Fissure CN III, IV, V1, VI Middle meningeal artery- orbital branch Recurrent meningeal artery Superior opthalmic vein Inferior Orbital Fissure Infraorbital artery, vein, and nerve (V2 branch) Optic Canal Optic nerve Opthalmic artery Speaking of the superior orbital fissure… Below SOF = IOF. Optic canal = more superior to SOF.

Skull Base Anatomy Review Key Openings Foramen spinosum Foramen ovale Foramen lacerum Foramen rotundum Foramen magnum Foramen of vesalius Jugular foramen Superior orbital fissure Inferior orbital fissure Optic canal Vidian canal Hypoglossal canal Pterygopalatine fossa

Skull Base Pathology Meningioma Chordoma Metastases Chondrosarcoma Myeloma Neuroma Schwannoma Vascular Aneurysm Chordoma Chondrosarcoma Dermoid tumors Epidermoid tumors Glomus tumors Chordomas like the clivus Chondrosarcomas like the cartilaginous endplates- petrooccipital suture Glomus tumors- jugular bulb, middle ear, carotid body Meningiomas- most common (20% of all brain tumors). But most = cerebral convexity, along and lateral to the falx. 10% clivus 20% sphenoid ridge Schwannomas almost always develop from sensory nerves. Because the olfactory and optic nerves do not have a Schwann cell layer, they do not develop these tumors. The most common intracranial schwannoma = acoustic neuroma- it develops from the vestibular nerve. Bilateral acoustic neuromas = pathogomonic for NF2. (90% of the time, schwannomas are solitary). The second most common intracranial schwannomas develop from the trigeminal nerve. Trigeminal schwannomas usually arise from the root or ganglion and occupy the middle fossa and, sometimes, the posterior fossa. Schwannomas of the other cranial nerves are rare.

Case 1 T1 post contrast MR showing extraaxial lesion arising from the middle cranial fossa. Heterogeneous enhancement. Low signal areas = flow voids or calcs. Coronal = involvement with skull base. Mass effect on temporal lobe.

Chondrosarcoma CT Findings: MRI Findings: Irregular, destructive mass Centered off midline Petro-occipital fissure Calcifications, 70%; “rings/arcs” MRI Findings: Low T1 signal, high T2 signal Enhance with contrast Scalloped, well circumsribed margins

Chondrosarcoma Origin: Location: Clinical: Preexisting cartilaginous lesion, synchondroses, cartilage endplates Location: Paranasal sinuses, skull base, parasellar region Long bones, pelvis, sternum, ribs Clinical: 45 yo, median age Classic, mesenchymal, or dedifferentiated Chondrosarcomas can occur anywhere in the skeletal system. Often = preexisting cartilaginous lesion like previously benign osteochondroma. In skull base = usually at cartilage endplates. E.g. petrooccipital suture. Location: read slide Clinical: Most commonly, patients are diagnosed with chondrosarcomas during the third or fourth decade of life. Males are affected more often than females. Chondrosarcomas can be divided into classic, mesenchymal, and dedifferentiated tumors. Mesenchymal, Dedifferentiated = high grade. Classic low grade = like chordoma. DDX: Chordoma- usually has marked bone destruction, midline (clivus) Chondrosarcoma = significant soft tissue component, little bone destruction, arcs/nodules of calcification, eccentric locations- often centered in framen lacerum.

Case 2 Sagittal T1-weighted MR image shows a large, hypointense soft-tissue mass that arises from the distal clivus with anterior extension into the nasopharynx (arrows) and extradural extension into the posterior fossa (arrowhead).

Chordoma CT/MRI Findings: DDx: Expansile lytic lesion, midline Well delineated mass arising from bone Large soft tissue component Variable calcification Anteroposterior extension Heterogeneous enhancement on T1, T2 Dark on T1, bright on T2 CT to assess degree of bone involvement. MRI to evaluate extension of tumor. CT Findings: The most characteristic appearance of intracranial chordoma is of a centrally located homogeneous soft tissue mass arising from the clivus and causing adjacent bone destruction. Calcification is common but variable. Areas of low attenuation within the soft tissue mass occasionally are found on CT, representing the myxoid and gelatinous material found on pathologic examination. CT reliably demonstrates petrous apex involvement and lysis of the skull base foramina. MRI Findings: Mass originating from midline with extension primarily in the anteroposterior axis rather than laterally. Well delineated. Expands bone in the early stage = indicator that it arises from bone, not from adjacent structures. Post gad = lobulated area, heterogeneous on T1 and T2 b/c of mucinous and gelatinous contents. DDX: Chondroma- similar appearance but extend more laterally into sellar and cerebellopontine angles. Clivus meningioma – homegeneous signal, dural attachment DDx: Chondroma Chondrosarcoma Clivus meningioma

Chordoma Origin Location Clinical Notochord remnants Clivus 35% Sacrum 50%, Vertebral bodies 15% Clinical age 30-70 Slow growing, locally aggressive CN VI- CN deficits Mets late Tx: surgery, radiation Contrast enhanced T1 spin echo image. Chordoma of the upper part of the clivus with posterior extension into the pontine cistern. Chordomas = benign tumor but has significant problems b/c of location, local invasion, recurrence. Origin: Notochord = early fetal axial skeleton. Gets surrounded by cartilage. Cartilage ossifies and notochord = squeezed out into intervertebral regions = nucleus pulposus of intervertebral disks. Can get remnants then, along any position of the neural axis- turn into chordomas. Location: read slide. Rare. <0.2% of all intracranial tumors. Clinical:read slide CN deficits: HA, dysphagia, facial pain, facial paresis, visual loss, hearing loss, and ataxia. CT to assess degree of bone involvement. MRI to evaluate extension of tumor. CT Findings: The most characteristic appearance of intracranial chordoma is of a centrally located homogeneous soft tissue mass arising from the clivus and causing adjacent bone destruction. Calcification is common but variable. Areas of low attenuation within the soft tissue mass occasionally are found on CT, representing the myxoid and gelatinous material found on pathologic examination. CT reliably demonstrates petrous apex involvement and lysis of the skull base foramina. MRI Findings: Mass originating from midline with extension primarily in the anteroposterior axis rather than laterally. Well delineated. Expands bone in the early stage = indicator that it arises from bone, not from adjacent structures. Post gad = lobulated area, heterogeneous on T1 and T2 b/c of mucinous and gelatinous contents.

Case 3 CT imaging demonstrates the extent of bony destruction (white and black arrows) by the tumor. The normal jugular foramen on the left (arrow head) is shown for comparison.

Glomus jugulare CT/MRI Findings: Glomus Tumor Glomus jugulare CT/MRI Findings: Center: jugular foramen Limit: hyoid bone Enhance w/ contrast Salt and pepper appearance on MRI Bone erosion Salt and pepper: multiple low signal intensity areas = flow voids in tumor. When large- erode bone.

Glomus Tumor Origin: Location: Clinical: Chemoreceptor cells 10% multiple glomus jugulare: jugular bulb glomus tympanicum: cochlear promontory; Clinical: Pulsatile tinnitus Hearing loss arrythmia, BP fluctuation Glomus tumors arise from chemoreceptor cells. These tumors are slow-growing hypervascular tumors that usually occur in the temporal bone. Location: read slide- check other places for them b/c = multiple. E.g. Carotid body Patients usually present with gradual hearing loss, unilateral pulsatile tinnitus, and lower cranial nerve palsies. Approximately 1-3% of gangliogliomas produce catecholamines, so can get arrythmia, BP fluctuation. May be locally invasive but rarely metastasize.

References Erdem E, et al, “Comprehensive Review of Intracranial Chordoma”, Radiographics 2003; 23: 995-1009. Grossman, R et al, Neuroradiology: The Requisites, Mosby, Philadelphia, 2003 Peretti P et al, “Chordoma”, www.emedicine.com/Radio/topic169.htm, 2005. Pluta R et al, “Glomus Tumors”, www.emedicine.com/med/topic2994.htm, 2006. Small J et al, “Chondrosarcoma”, http://brighamrad.harvard.edu/education/online/tcd/tcd.html. Weissleder, R et al, Primer of Diagnostic Imaging, Mosby, Philadelphia, 2003 http://www.med.wayne.edu/diagRadiology/Anatomy_Modules/axialpages/Home_Page.html

Jennings Pond, Chester, CT